fix(ci): isolate web smoke dependencies

[hongjr03]

Summary

• Move @vscode/test-web and its Playwright browser dependency into a private editors/vscode/test-web package.
• Make the VS Code Web Smoke job install and cache that package separately.
• Keep extension package installs free of browser install scripts for package jobs, including Alpine.

Testing

• actionlint .github/workflows/ci.yml .github/workflows/release.yml
• npm ci in editors/vscode
• npm ci in editors/vscode/test-web
• npm run typecheck
• npm --prefix test-web run typecheck
• npm test
• npm run bundle:browser
• npm run bundle:test-web
• npm --prefix test-web test reached the runner after typecheck, then failed locally while downloading VS Code Stable with ECONNRESET from update.code.visualstudio.com.